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Real-Time Relationships in Intraluteal Release among Prostaglandin F₂, Endothelin-1, and Angiotensin II During Spontaneous Luteolysis in the Cow¹

Department of Agricultural and Life Science³ The Field Center of Animal Science & Agriculture,⁴ Obihiro University of Agriculture and Veterinary Medicine, Obihiro 080-8555, Japan Department of Animal Science,⁵ University of Peradeniya, Peradeniya 20400, Sri Lanka

It is well known that prostaglandin F₂ (PGF₂) is a physiological luteolysine, and that its pulsatile release from the endometrium is a luteolytic signal in many species. There is now clear evidence that the vasoactive peptides endothelin-1 (ET-1) and angiotensin II (Ang II) interact with PGF₂ in the luteolytic cascade during PGF₂-induced luteolysis in the cow. Thus, we investigated the local secretion of PGF₂, ET-1, and Ang II in the corpus luteum (CL) and their real-time relationships during spontaneous luteolysis in the cow. For this purpose, an in vivo microdialysis system (MDS) implanted in the CL was utilized to observe local secretion changes within the CL microenvironment. Each CL of cyclic Holstein cows (n = 6) was surgically implanted with MDS capillary membranes (18 lines/6 cows) on Day 15 (estrus = Day 0) of the estrous cycle. The concentrations of PGF₂, ET-1, Ang II, and progesterone (P) in the MDS samples were determined by enzyme immunoassays. The intraluteal PGF₂ secretion slightly increased from 12 h after the onset of luteolysis (0 h) and drastically increased (by about 300%) from 24 h. Intraluteal ET-1 secretion increased from 12 h. Intraluteal Ang II secretion was elevated from 0 h and was maintained at high levels (about 180%) toward estrus. In each MDS lines (in the same microenvironment) within the regressing CL, the local releasing profiles of PGF₂, ET-1, and Ang II CL positively correlated with each other (P < 0.05) at high proportions in 18 MDS lines (PGF₂ vs. ET-1, 44.4%; PGF₂ vs. Ang II, 55.6%; ET-1 vs. Ang II, 38.9%). In contrast, there was no clear relationship among these substances released into different MDS lines implanted in the same CL (with different microenvironments). In conclusion, we propose that the increase of PGF₂, ET-1, and Ang II within the CL during luteolysis is a common phenomenon for both PGF₂-induced and spontaneous luteolysis. Moreover, this study illustrated the in vivo relationships in intraluteal release among PGF₂, ET-1, and Ang II during spontaneous luteolysis in the cow. The data suggest that these vasoactive substances may interact with each other in a local positive feedback manner to activate their secretion in the regressing CL, thus accelerating and completing luteolysis.

¹ This study was supported by the Grant-in-Aid for Scientific Research of the Japan Society for the Promotion of Science (JSPS) and the 21st Century COE Program (A-1), Ministry of Education, Culture, Science and Technology of Japan. T.J.A. and M.P.B.W. are postdoctoral fellows supported by JSPS. M.M is supported by the COE Program.

² Correspondence. FAX: 81 155 49 5593; akiomiya{at}obihiro.ac.jp

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